Automatic control equipment



Dec. 4, 1945. Y 2,390,345.

AUTOMATIC CONTROL EQUIPMENT Fil ed March 22, 1944 s Sheets- Sheet 1Inventor:

Herman Ban b5 W His Attorney.

Dec. 4, 1945. H. BANY 2,390,345

AUTOMATI C CONTROL EQUIPMENT Filed March 22, 1944 3 Sheets-Sheet 2Imventor: Herman Bang,

Patented Dec. 4, 1945 2,390,345 AUTOMATIC CONTROL EQUIPMENT Herman Bany,Lansdowne, Pa., asslgnor to General Electric Company, a corporation ofNew York Application March 22, 1944, Serial No. 5274337 20 Claims. (Cl.171-123) My invention relates to automatic control equipments andparticularly to equipments for automatically synchronizing a synchronousfrequency conventer under different electric conditions of the twoelectric systems which are arranged to be interconnected by theconverter.

One object of my invention is to provide an improved arrangement forcontrolling the relative frequencies of a synchronous frequencyconverter and one of the electric systems to which it is to be connectedso as to establish a frequency difference and phase relation of thevoltages existing between the converter and the system which will allowthe converter to pull into step when it is connected to the system.

Another object of my invention is to provide an improved arrangement forsynchronizing two synchronous frequency converters located in twosubstations at different points on an electric system, in such a mannerthat a minimum number of control wires is required between the twosubstations.

A further object of my invention is to provide an arrangement forautomatically effecting the synchronization of asynchronous frequencycon- Verter to the two electric systems to which it is to be connected,in different ways depending upon the electric conditions of the twosystems.

A still further object of my invention is to provide an arrangement forautomatically synchronizing a synchronous converter in parallel withanother synchronous converter in different ways depending upon whetheror not the high and low frequency electric systems to which theconverters are respectively connected are separate systems or areinterconnected.

My invention will be better understood from th following descriptionwhen taken in connection with the accompanying drawings, the threefigures of which, when placed side by side, diagrammatically illustratean electric system comprising a plurality of synchronous frequencyconverter control equipments embodying my invention.

In the accompanying drawings, Figs. 1 and 2, and the left-hand portionof Fig. 3, diagrammatically illustrate the control apparatus forstarting and synchronizing a synchronous irequency converter at onesubstation A of an electric system, and the right-hand portion of Fig. 3diagrammatically illustrates a portion of similar control apparatus forstarting and synchronizing a synchronous frequency converter at anothersubstation B of the electric system. As shown, the two substations A andB are respectively located at different points of the electric systemand have respectively tne nigh frequency cases I and 2 and the lowfrequency buses 3 and 4. inc high ire--v quency bus I at the substationA is normally energized by a prime moverdriven generator :1 and isarranged to be connected by means or a suitable switch u to a tie lineI. blmllally, the high irequency bus 2 at the substation 1:5 is normallyenergizeu by a prime mover driven generator is and is arranged to beconnected by means 01 a suitable switch a to tne tie nne I so that whenboth of the switches e and a are simultaneously closed the highfrequency buses and 2 at the two stations are tied together.

1116 low lrequency bus 3 at the substation A is arranged to be connectedby means or a suitable switch w to a tie line H, and the 10W lrequencybus 4 at the substation B is arranged to be connected by means of asuitable swltcn II to the tie line H so that when both 01 switches Illand [2 are simultanously closed the buses a and 4 at the two stationsare tied to ether. line buses 3 and 4 also are arranged to be suppliedwith electric 'eneigy Irom one or more other sources of current, notshown, and may or may not be interconnected by other means than tne tieline I I.

At the substation A, the buses l and 3 are arranged to be interconnectedby means of a synchronous irequency converter l4 comprising a highfrequency synchronous machine In which is arranged to be connected tothe high frequency bus I by means or a suitable circuit breaaer l6 and a10W frequency synchronous machine 11 which is arranged to be connectedto the low frequency bus s by means or a. suitable circuit breaner It.The synchronous frequency converter I4 also is provided with a directconnected exciter l9 and a ull'eCD connected variable speed inductionmotor 2d tor starting and varying the speed of the converter during thesynchronization thereof. The converter 14 is also provided with asuitable frame Si'llitlllg motor Al for varying the position of thestator of one of the synchronous machines of the converter relative tothe position of the stator of the other synchronous machine.

At the substation B, the buses 2 and 4 are arranged to be interconnectedby means of a similar synchronous irequency converter 22 comprising ahigh frequency synchronous machine 23 which is arranged to be connectedto the high frequency bus 2 by means of a suitable circuit breaker 24and a low frequency synchronous machine 25 which is arranged to beconnected to the low frequency bus 4 by means of a suitable circuitbreaker 26. The synchronous converter 22 also is provided with a directconnected exciter 21, a variable speed induction motor 28 for startingand varying the speed of the converter while the converter is beingsynchronized, and with a frame shifting motor 29.

Since the control apparatus for each of the two converters is the same,I have shown in detail only the control apparatus for the converter I4and have shown only that portion of a similar control apparatus for theconverter 22 as is deemed necessary for a complete understanding of myinvention.

When a converter is being placed in service, it is first started byconnecting its starting motor to a suitable source of current and thencontrolling the speed of the starting motor so that one of thesynchronous machines of the converter can be automatically synchronizedwith its associated bus. As will be pointed out later, when a converteris being placed in service the first synchronous machine thereof to besynchronized depends upon the electric conditions of the buses at thetime that the converter is being started and whether or not the otherconverter is in service. 'After the first machine of a converter hasbeen synchronized, the other machine is then synchronized in a mannerdepending also upon the electric condition ofthe buses.

When the synchronous converter I4 is being placed in service, a switch30 is first closed to connect the starting motor 20 to the bus I.Therefore, it will be observed that before the converter l4 can bestarted the associated high frequency bus I has to be energized by theassociated generator 5. When the starting motor 20 has accelerated theconverter I4 to a speed near the normal synchronous speed of theconverter, the field windings 3| and 32 of the synchronous machines land II respectively are connected to the exciter ill by the fieldswitches 33 and 34 so that the voltages of these machines build up tosubstantially their respective normal values.

If the other synchronous frequency converter 22 is not in service at thetime the converter I4- is started, the high'frequency machine I5 is thefirst synchronous machine of the converter l4 to be synchronized. Thisresult is accomplished by automatically controlling the position of amotor operated rheostat 35 in the secondary circuit of the startingmotor 20 in response to the difference in the frequencies of thesynchronous machine l5 and the bus I. Since such frequency differenceresponsive means are well known in the art and the details of such anarrangement form no part of my present invention,'I have representedsuch means merely by a suitably labeled rectangle 36. My prior Patent2,252,456, granted August 12, 1941, and assigned to the assignee of thisapplication, discloses the details of a suitable speed controlarrangement which may be used for controlling the speed of the startingmotor 20 in the desired manner. As soon as the proper phase andfrequency relation is established between the voltages of the highfrequency synchronous ma- I chine l5 and the bus I by the speed controlarrangement, a suitable automatic synchronizer 31 is arranged to effectthe closing of the circuit breaker I6 so as to connect the synchronousmachine I5 to the bus I. One type of automatic synchronizer which may beused is disclosed in Letters Patent 2,009,097, granted July 23, 1935, onan application filed by H. T. Seeley and assigned to the same assigneeas this application.

Since the details of the automatic synchronizer 31 form no part of mypresent invention, I have represented the automatic synchronizer merelyby a suitably labeled rectangle.

The closing of the circuit breaker I6 is arranged to effect the openingof the switch 30 so as to disconnect the starting motor 20 from the busI and also to render the frequency responsive means 36 and the automaticsynchronizer 31 inoperative. The closing of the circuit breaker l6 alsorenders operative a suitable frequency difference responsive means 39,which is similar to the frequency difference responsive means 36 exceptthat it is responsive to the difference between the frequencies of thesynchronous machine H and the bus 3. Also, the closing of the circuitbreaker l6 renders operative a suitable automatic synchronizer 40similar to the automatic synchronizer 3? except that it is responsive tothe phase and frequency relation of the voltages of the synchronousmachine I! and the bus 3. The frequency difierence responsive means 39controls the speed of the prime mover driven generator 5 so as toestablish the proper phase and frequency relation between the voltagesof the synchronous machine I1 and the bus 3 to cause the automaticsynchronizer 40 to operate and effect the closing of the circuit breakerl8 between the synchronous machine I! and the bus3.

If at the time the converter I4 is being placed in service the lowfrequency bus 3 is not energized, the synchronous machine I! issynchronized in the following manner. After the circuit breaker I6 isclosed toconnect thesynchronous machine l5 of the converter 14 to thebus 1, the field switch 34 is opened so as to disconnect the fieldwinding 32 from the exciter I9, then the circuit breaker I8 is closedwhile the field winding 32 is deenergized, and then the field switch 34is reclosed to again energize the field winding 32.

When a synchronous frequency converter is being connected in parallelwith another frequency converter which is already in service, it is'necessary in order to maintain the proper parallel operation of the twoconverters that the second machine to be placed in operation shall besynchronized only when there is a predetermined space relationshipexisting between all of the field poles of the two converters. In orderto accomplish this result, I provide an arrangement of apparatus wherebythe first machine of the second converter to be placed in service can besynchronized only when a predetermined space relationship exists betweenthe rotors of that machine and the corresponding machine of theconverter that is already in service. Furthermore, when a secondconverter is being started, the particular machine thereof that issynchronized first depends upon the electric condition of the buses. Inthe particular arrangement shown-in the drawings, if the low frequencybuses 3 and 4 are tied together when the second converter is beingstarted, the low frequency machine thereof is synchronized first. If,however, only the high frequency buses I and 2 are tied together orneither the buses l and 2 nor the buses 3 and 4 are tied together, thehigh frequency machine of the second converter to be placed in serviceis synchronized first.

Therefore, if the converter 22 in the arrangement shown in the drawingsis in service when the converter I4 is being placed in operation, thesynchronous machine I! is synchronized first if the buses 3 and 4 aretied together, but the synchronous machine I4 is synchronized first ifonly the high frequency buses I and 2 are tied together or the highfrequency buses I and 2 and the low. frequency buses are notrespectively connected together. As a means for indicating that thebuses I and 4 are tied together, I provide at one o! the substations,which in the particular arrangement shown in the drawings is thesubstation A, a synchronism check relay 42 which is connected acrosscorresponding phase conductors of the buses 3 and 4 and which isarranged to close its contacts 43 only when the frequencies of the twobuses 3 .and 4 are the same and the phase difference betweencorresponding voltages of these two buses is less than a predeterminedvalue. Also, I provide at the substation A the voltage relays 44 and 45which are respectively responsive to predetermined voltages of the buses5 and 4. The relay 45, when energized, and the contacts 43 of thesynchronism check relay 42 are respectively arranged to completeenergizing circuits for a control relay 45, which when energizedindicates that the buses 3 and 4 are electrically tied together eitherby the switches I and I2 and the tie line I I or by some other means notshown. Furthermore, since an open circuit or a short circuit on thepilot wires 41 and 40, which connect the relays 43 and 45 at thesubstation A with the bus 4 at the substation B effects adeenergizationof the voltage relay 45, the energization of the control relay 45 isalso an indication that the pilot wires 41 and 48 are in normaloperating condition.

For controlling the operation of the control apparatus at the substationB in accordance with the voltage of the bus 4, I provide a voltage relay49 which is responsive to the voltage thereof. In order to indicate thatthe two high frequency buses I and 2 are tied together by the switchesand 9 and the tie line 1, I provide, at the substations A and Brespectively, the control relays 50 and 5i which are both arranged to beenergized when either converter is in operation and the buses I and 2are not tied together. This re suit is accomplished by connecting theoperating coils of these two-relays 50 and 5I in series with thecontacts 54 and 55, which are respectively closed when the switches 5and 9 are open and which are connected in parallel by the pilot wires 52and 53 which interconnect the two substations. At the substation A, theseries circuit for the relays 50 and SI is arranged to be completedacross a battery B by means of a pilot wire 55,

which interconnects the two substations A and B and by the contacts I04and I05 of a master relay 51, which is energized whenever the converterI4 is in operation. The circuit of the relays 50 and 5! is arranged tobe connected across a battery B" at the substation B by means of a pilotwire 53 which interconnects the two substations A and B and the contactsI04 and I05 of a master relay 58, which is energized when the converter22 at the substation B is in operation.

For indicating that both of the converters are running at substantiallysynchronous speed, I provide at the substations A and B, respectively,the relays 5i and 52 which are both arranged to be energized when eitherof the converters is operating and the other is not operating. Thisresult is accomplished by connecting across the pilot wires 55 and 58the operating windings of the relays GI and 52 in series with theparallel connected contacts 53 and 54 of the exciter voltage relays 55and 55 at the substations A and B, respectively. The relay 55 isconnected so as to be responsive to the voltage of the exciter I9 and isarranged to open its contacts 03 when the voltage of the exciter II isabove a predetermined subnormal value. The relay 40 is similarlyarranged so that it responds to the voltage of the exciter 21 and isarranged to open its contacts 54 when the voltage of the exciter 21 isabove a predetermined subnormal value. The contacts 53 and 54 areconnected in parallel by the pilot wires 51 and 55 which interconnectthe two substations A and B. Since the voltages of the exoiters I0 and21 are high enough to eflec't the simultaneous opening of the contacts53 and 54 only when both of the synchronous converters are in operation,it will be'evident that the relays ll and 52 are allergized when onlyone of the converters is in operation.

When the relays 50 and 5| at the substation A are simultaneouslydeenergizcd, an energizing circuit is completed for a control relay 10.Therefore when the relay 10 is in its energized position it indicatesthat the high frequency buses I and 2 are tied together and that both ofthe converters are operating at substantially synchronous speed. Therelays 5I and 52 at the substation B are arranged to.complete anenergizing circuit for a control relay 1I under similar conditions ofthe buses I and 2 and the converters I4 and 22.

For indicating that the low frequency buses 3 and 4 are tied togetherand both of the converters are operating, I provide the control relays13 and 14 at the substations A and B, respectively, and connect theoperating windings thereof and the parallel connected contacts 15, 15and 11 of the relays 55, 55 and 45, respectively, in series across thepilot wires 55 and 50. Since the contacts 15 of the exciter voltagerelay 55 are closed when the converter I4 is not in operation and thecontacts 15 of the exciter voltage relay 55 are closed when theconverter 22 is not in operation and the contacts 11 of the relay 45 areclosed when the buses 3 and 4 are not tied together, it is evident thatwhile any master relay is energized the relays 13 and 14 are deenergizedonly when the buses 3 and 4 are tied together and both of the convertersI4 and 22 are also in operation.

For obtaining an indication that the rotors of the two converters I4 and22 are in proper space relationship with respect to each other forsynchronizing, I provide at the substation A a control relay which, whenthe converter I4 is being started as the second machine, is arranged tobe'connected in series with the contact making devices 82 and 83respectively mounted on the shafts of the converters I4 and 22 if thesynchronous machine ii: is synchronized first, and in series with thecontact making devices 84 and 85 also respectively mounted on the shaftsof the converters I4 and 22 if the synchronous machine I1 issynchronized first. A similar relay 0| is provided at the substation Bfor indicating the proper space relationship of the rotors While theconverter 22 is being started as the second machine. The contact makingdevices 82 to 85, inclusive, may be of any suitable construction wherebythey respectively make contact when a predetermined portion of the rotorsurface of the associated converter is passing a predeterminedstationary point during each revolution of the rotor. The length of eachcontact depends upon the load angle and the polar arc'of the associatedmachine. Consequently, the number of mechanical degrees during eachrevolution of the associated converter that the contacts 82 and 83 canmake contact to eflect the proper synchronization is less than thenumber of mechanical degrees the contact devices 84 and 85 can makecontact. The condensers 88 and 81 are respectively connected in parallelwith th operating windings of the relays 80 and 8| so that after theserelays have picked up they remain in their picked-up positions for asufllcient length of time to complete the synchronizing operationinitiated thereby.

In a manner which will be more fully described hereinafter, the relay 80is arranged to be placed under the control of the contact making devices82 and 83 during the synchronizing operation of the converter I4 when itis started as the second converter and the high frequency buses I and 2are tied together electrically and the low frequency buses 3 and 4 arenot tied together or are deenergized, and is arranged to be placed underthe control of the contact making devices 84 and 85 during thesynchronizing operation of the converter I4 when it is started as thesecond converter and the low frequency buses 3 and 4 are tied together.The circuit of the relay 80 also includes at the substation A'thecontacts 239 of a relay 88 which is so connected that it is arranged tobe energized whenever the associated high frequency machine I5 is beingsynchronized and the contacts I98 of a relay 89 which is so connectedthat it is arranged to be energized when the associated low frequencymachine I! is being synchronized. At the substation B, the circuit ofthe relay 80 includes the contacts 208 of a relay 90 which is arrangedto be energized only while the high frequency machine 23 -is beingsynchronized and the contacts 209 of a relay 9I which is arranged to beenergized only while the low frequency machine 25 is being synchronized.The order in which the relays 88 and 89 or 90 and 9| are energized whilethe associated converter is being placed in service depends upon theelectric condition of the buses and whetheror not the other converter isin service.

The relay 8| at the substation B is arranged to be connected in serieswith either the contact making devices 82 and 83 or the contact makingdevices 84 and 05 in a similar manner across the battery B at substationA while the converter 22 is being started as the second converter.

The frame shifting means of each converter is normally maintained in itsneutral position but is arranged to be operated to effect thesynchronization of the associated high frequency machine when theassociated converter is started while the other converter is inoperation and both the high frequency buses I and 2 and the lowfrequency buses 3 and 4 are respectively tied together. The operation ofthe frame shifting motor 2I of the converter I4 under such electricconditions of the buses is controlled by a suitable phase responsivearrangement 95 which is connected to the high frequency synchronousmachine I5 and the high frequency bus I so that the contacts 96 areclosed to effect the movement of the frame shifting motor 2|" in onedirection in response to the voltage of the machine I5 leading thevoltage of the bus I, and the contacts 91 are closed to effect themovement of the frame shifting motor in the opposite direction inresponse to the voltage of the machine I5 lagging the voltage of the busI, and the contacts 98 and 89 are simultaneously closed, when the twovoltages are substantially in phase. Since the details or such a phaseresponsive arrangement constitute no part of my present invention andfurthermore are disclosed in detail in my prior Patent 2,004,776,granted June 11, 1935, and assigned to the assignee of this application,I have represented such a phase responsive arrangement 95 merely by asuitably labeled rectangle surrounding the contacts 96-99, inclusive.The operation of the embodiment of my invention shown in the drawingswill be described by describing only the operation of the controlapparatus for the converter I4 at the substation. I

A under different electric conditions of the buses I to 4, inclusive,and under different operating conditions of the other converter 22 sincethe control apparatus for the converter 22 at the substation B functionsin a similar manner to synchronize the converter 22 under similarelectric conditions of the buses I to 4, inclusive, and under similaroperating conditions of the other converter I4.

Buses 1 and 2 energized and not tied together; buses 3 and 4 energizedand tied together; and no converter in operation It will be assumedfirst that the switches 5 and 9 are open so that the buses I and 2 arenot connected together by the tie line I and that the switches I0 and I2are closed so that the buses 3 and 4 are connected together by the tieline II. Under such conditions, the voltage relays 44 and 45 areenergized, and the contacts 43 of the synchronism check relay 42 areclosed so that the control relay 46 is also energized.

When it is desired to place the converter I4 in service, an-associatedmanually controlled start switch I00 is closed to complete an energizingcircuit for the associated master relay 51 from the positive terminal ofthe battery B through the contacts of the start switch I00, winding ofthe master relay 51, conductor IOI, contacts I02 on the motor operatedrheostat 35 which are closed only when the rheostat is in apredetermined starting osition, to the negative terminal of the batteryB. The closing of the contacts I03 of the master relay- 5'! completes ashunt circuit around the contacts I02 of the rheostat 35. The contactsI04 and I05 of the master relay 51 respectively connect the pilot wires58 and 56 to the positive and negative terminals of the battery B sothat the relays 50 and 5| are energized since the auxiliary contacts 54and 55 on the switches 6 and 9 respectively are closed. The closing ofthe contacts I04 and I05.of the relay 5! also completes an energizingcircuit for the relays BI and 62 through the pilot'wires 61 and 68 inparallel, and an energizing circuit for the control relays I3 and I4-through the pilot wire I06 and the series connected contacts 15 of therelay 65 and also through the pilot wire I01 and the contacts I6 of therelay 68.

The closing of the contacts I08 of the master relay 5'! completes anenergizing circuit for the operating winding of the starting switch 30for the starting motor 20 from the positive terminal of the battery Bthrough the operating winding of the switch 30, conductor I09, contactsI08 of relay 5'1, conductor IIO, contacts III on circuit breaker I6,conductor 2', contacts 3' on cirthe bus I. At the instant of starting,the secondary circuit of the motor 23 includes a starting resistor IIand the adjustable rheostat 35. As soon as the switch 33 closes, thestarting motor 23 immediately starts to accelerate the rotor of V theconverter I4 and the starting current through the primary winding of thestarting motor 26 is suflicient to cause the current relay III in theprimary circuit of the motor to open its contacts H2 and maintain themopen until the converter I4 has been accelerated to approximately itssynchronous speed. When the contacts H2 are reclosed in response to theconverter reaching substantially synchronous speed, an energizingcircuitis completed for the operating coil of a suitable switch H3 to shortcircuit the starting secondary resistance H3. This energizing circuit isfrom the positive terminal of the battery B through the contacts I I5 ofmaster relay 51, conductor H6, contacts H1 which are arranged to beclosed, a predetermined time after the switch 30 closes, contacts H2 ofthe current relay I II,

operating winding of switch H3 to the negative terminal of battery B.The closing of the auxiliary contacts H8 of the switch H3 completes ashunt circuit around the contacts H2 of the current relay III. Theclosing of the auxiliary contacts H9 of the switch H3 completes anenergizing circuit for the operating windings of the field switches 33and 34 to connect the field windings 3| and 32 of the synchronousmachines I5 and I1, respectively, to the exciter I9. The energizingcircuit for the operating winding of the field switch 33 is from thepositive terminal of the battery B through contacts H5 of relay 51,conductor H6, contacts H9 of switch H3, conductor I20, winding of fieldswitch 33 to the negative terminal of the battery B. The energizingcircuit for the winding of the field switch 34 is from the positiveterminal of the battery B through contacts H5 of relay 51, conductor H6,contacts H9 of switch H3, conductor I23, auxiliary contacts I 2I oncircuit breaker I6 in parallel with contacts I22 of relay 44, conductorI23, winding of field switch 34'to the negative terminal of battery B.The closing of the auxiliary contacts I24 of the field switch 33 and ofthe auxiliary contacts I25 of the field switch 34 completes shuntcircuits around the contacts H9 of switch I I3. I

The closing of the time delay contacts I26 of the switch H3, whichcloses a predetermined time after the main contacts of the switch areclosed, completes an energiz ng circuit for the control relay 521 if atthe same time the voltage of the exciter it has built up to a sufficientvalue to effect the operation of the voltage relay 65. This energizingcircuit for the control relay IE1 is from the positive terminal of thebattery B through contacts H5 of relay 51, conductor H5, contacts I28 ofrelay 65, conductor I29, contacts I33 of current relay I I i, time delaycontacts l26 of switch H3, w ndin of relay I21 to the negative terminalof battery B. The closing of the contacts I3I of the relay I21 completesa locking circuit for the relay from conductor I I6 directly to thewinding of the relay.

Since the relay 13 i energized during the entire starting operation ofthe connection I4 under the assumed electric conditions of the buses,the closing of the contacts I32 of the relay I21 completes an energizingcircuit for the control relay 88 from the positive terminal of thebattery B through contacts H5 of relay 51, conductor H6, contacts I32 ofrelay I21, conductor I33, auxiliary contacts I34 on circuit breaker I3,conductor I35, winding of relay 33, contacts I36 of relay 89, conductorI31, contacts I33 of relay 13 to the negative terminal of the battery B.

The closing of the contacts I43 and I of the relay 63 renders thefrequency difference responsive means 36 and the automatic synchronizer31 operative by connecting them tothe bus I and to the synchronousmachine I5. If the frequency of the synchronous machine I5 is below thefrequency of the bus I more than a predetermined amount, the frequencydifierence responsive means 36 closes its contacts I43 and completes acircuit for the motor I5I of the motor operated rheostat 35 from thepositive terminal of the battery B through contacts H5 of relay 51,conductor H6, contacts I32 of relay I21, conductor I33, contacts I44 ofrelay 88, conductor I45, contacts I46 of starting switch 33, conductorI41, contacts I43 of frequency difference responsive means 36, conductorI48, limit switch I49 on rheostat 35, field winding I53 and armaturewinding of motor I5I to the negative terminal of the battery B. Thisenergizing circuit causes the motor I5I to operate in a direction todecrease the amount of resistance in the secondary circuit of thestarting motor 20 so as to increase the speed thereof and the frequencyof the synchronous machine I 5. If the frequency of the synchronousmachine I5 is above the frequency of the bus I, or is less than the busfrequency but the frequency difference is below a predetermined value,the frequency difference responsive means 36 closes its contacts I52 andcompletes an energizing circuit for the motor I5I of the motor operatedrheostat 35 from the positive terminal of the battery B through contactsH5 of relay 51, conductor H6, contacts I32 of relay I21, conductor I33,contacts I44 of relay 88, conductor I45, contacts I46 of starting switch33, conductor I41, contacts I52 of frequency difference responsive means36, conductor I53, limit switch I53 of rheostat 35, field winding I54and armature winding of motor I5I to the negative terminal of battery B.This energizing circuit causes the motor I5I to operate in a directionto increase the amount of resistanc in the secondary circuit of themotor 20 so as to decrease the speed thereof and th frequency of thesynchronous machine I5.

When the difference between the frequencies of the synchronous machinei5 and the bus I is less than a predetermined value and a predeterminedphase relation also exists between the voltages of the synchronousmachine l5 and the bus l, the automatic syncliroziizer closes itscontacts W5 and completes an energizing circuit for the clos ng coil ofthe circuit breaker i6 so as to connect the synchronous machine i5 tothe bus l. The energizing circuit for the closing coil of the circuitbreaker i6 is from the positive terminal of the battery B throughcontacts H5 of relay 51, conductor Ht, contacts l3? of relay I21,conductor I33, contacts I56 of relay 88, conductor I51, contacts I55 ofautomatic synchronizer 31, conductor I58, contacts I59 of relay 1!](which is deenergized because relays 5i) and 6| are energized under theassumed electric conditions), conductor I63, contacts I6l of relay l3,conductor I62, closing coil of circuit breaker I6 to the negativeterminal of batery B.

The opening of the auxiliary contacts III on the circuit breaker I6interrupts the heretofore described energizing circuit for the operatingcoil of the starting motor switch 36 so that this switch is opened todisconnect the starting motor 20 from the bus I. The opening of theauxiliary contacts II1 on the switch 30 effects the opening of the shortc rcuiting switch II3 so that the starting resistor H is reconnected inseries with the secondary winding of the starting motor 20. The closingof the aux liary contacts I89 on the switch 30 completes a circuit forthe motor I5I of the motor operated rheostat 35 through either the limitswitch I90 and the field winding I50 in series or the limit switch I9Iand the field winding I54 in series, depending upon the position of themovable arm-of the rheostat 35 so that the rheostat is restored to itsnormal starting position, in which position the contacts I02 are closed.

The opening of the auxiliary contacts I34 on the circuit breaker I6interrupts the heretofore.

described energizing circuit of the relay 88 so that it becomesde-energized. and by opening its contacts I40 and I, the relay 88renders the frequency difference responsive means 36 and the automaticsynchronizer 31 inoperative. The closing of the auxiliary contacts I64on the circuit breaker I6 completes an energizing circuit for thecontrol relay 89 from the pos tive terminal of the battery B throughcontacts II5 of relay 51, conductor II6, contacts I32 of relay I 21,conductor I33, auxiliary contacts I64 on circuit breaker I6, conductorI65, winding of relay 89, aux liary contacts I66 on circuit breaker I8to the negative terminal. of the battery B.

The closing of the contacts I61 and I68 of relay 89 renders thefrequency difference responsive means 39 and the automatic synchronizer40 operative by connect ng them to the synchronous machine I1 and to thebus 3. If the frequency of the synchronous machine I1 is higher than thefrequency of the bus 3 or is lower than this bus frequency, but thefrequency difference is less than a predetermined value. the frequencydifference responsive means 39 closes its contacts I10 and completes anenergizing circu t for a prime mover governing motor I'II so that iteffects a decrea e in the frequency of the synchronous machine I1 bydecreasing the frequency of the bus I. This energizing circuit for themotor I'll is from the positive terminal of the battery B throughcontacts II6 of relay 51. conductor II 6, contacts I32 of relay I21,conductor I33, contacts I12 of relay 89, conductor I13, auxiliarycontacts I14 on circuit breaker I 6, conductor I15. contacts I18 ofrelay 50, conductor I11, contacts I10 of frequency difference responsivemeans 39, field winding I18 and armature winding of motor "I to thenegative terminal of the battery B.

If the frequency of the machine I1 is lower than the frequency of thebus 3 by more than a predetermined amount, the frequency differenceresponsive means 39 closes its contacts I80 and completes an energizingcircuit for the prime mover governing motor Ill 50 that it effects anincrease in the frequency of the machine I1 by increasing the frequencyof the bus I. This operating circuit for the motor I1I is from thepositive terminal of the battery B to conductor I11 in the mannerheretofore described, then through contactsl80 of frequency differenceresponsive means 39, field winding I8I and armature windi g of motor I1Ito the negative terminal of the battery B.

Whenthe proper phase and frequency difference relations have beenestablished between the voltages of the synchronous machine I1 and thebus 3 in response to the operation of the frequency differenceresponsive means 39, the automatic synchronizer 40 closes its contactsI83 and completes an energizing circuit for the closingcoil of thecircuit breaker I8 so that the synchronous machine I1 is connected tothe bus 3. Theenergizing circuit for the closing coil of the circuitbreaker I8 is from the positive terminal of the battery B throughcontacts II5 of relay 51, conductor II6, contacts I32 of relay I21,conductor I33, contacts I84 of relay 89, conductor I85, contacts I83 ofautomatic synchronizer 40, conductor I86, auxiliary contacts I81 oncircuit breaker I6, conductor I88, closing coil. of circuit breaker I8to the negative terminal of g the battery 3'.

The opening of the auxiliary contacts I66 on the circuit breaker I8interrupts the heretofore described circuit for the control relay 89,which in turn by opening its contacts I61 and I 68 renders the frequencydifference responsive means 39 and the automatic synchronizer 40inoperative to control the prime mover governing motor I1I.

Buses 1 and 2 energized and not tied together; Buses 3 and 4 energizedand tied together; and one converter in operation It will now be assumedthat when the converter I4 is being placed in operation that theswitches 6 and 9 are open so that only the buses 3 and 4 aretiedtogether and that the converter 22 has been interconnected between thebuses 2 and 4. The closing of the start switch I 00 effects, in themanner heretofore described, the connection of the starting motor 20 tothe bus I and the acceleration ofthe converter I4 to approximatelysynchronous speed and the energization of the exciter voltage relay 65.Since under the assumed electric conditions the contacts 16 of theexciter voltage relay 66 at the substation 13 are open and also thecontacts" of the control relay 46 are open, the opening of the contactsof th exciter voltage relay 65 at the substation A effects thedenergization of the relays 13 and "so that when the relay I21 becomesenergized in response to the converter I4 reaching substantiallysynchronous speed, a circuit is completed for the control relay 89 fromthe positive terminal of the battery B through contacts II5 of relay 51,conductor II6, contacts I I32 of relay I21, conductor I33, contacts I95of voltage relay 44, conductor I96, contacts I91 of relay 13, conductorI65, winding of relay 89, auxiliary contacts I66 on circuit breaker I8to the negative terminal of battery B.

The closing of the contacts I98 of the relay 89-completes an energizingcircuit for the relay 80 from the positive terminal of the battery B" atthe substation B through contact-s I99 of relay 9|, contacts 200 ofrelay 90, contacts 20I of relay 14, contact making device 85, pilot wire202, contact making device 84 at substation A,

conductor 203, contacts 204. of relay 13, conductor 205, contacts I 98of relay 89, winding of relay 80 and condenser 86 in parallel, pilotwire 201, contacts 208 of relay 90 at substation B", contacts 209 ofrelay 9I to the negative terminal of the battery B. The relay 80therefore can be energized only when the positions of the rotors of theconverters and 22 are such as to effect the simultaneous closing of thecontacts of the contact making devices 84 and 85.

The closing of the contacts I61 and I68 of the relay 89 renders thefrequency difference responsive means 39 and the automatic synchronizer40 operative by connecting them to the synchronous machine I1 and thebus 3. If the frequency of the machine I1 is higher than the frequencyof the bus 3 or is lower than this bus frequency, but the frequencydifference is less than a predetermined value, the frequency differenceresponsive means 38 closes its contacts 2H! and completes an operatingcircuit for the rheostat motor II so as to increase the secondaryresistance of the motor 20 and thereby effect a decrease in the speed ofthe converter [4. This operating circuit for the motor I5I is from thepositive terminal of the battery B through contacts II5 of relay 51,conductor II6, contacts I32 of relay I21, conductor I33. contacts 2 ofrelay 89, conductor I45, auxiliary contacts I46 on starting switch 30,conductor I41, contacts 2! of frequency difference responsive means 39,conductor I53, limit switch I53 on rheostat 35, field winding I54 andarmature winding of motor I5I to the negative terminal of battery B.

If the frequency of the synchronous machine I1 is below the frequency ofthe bus 3 more than a predetermined amount, the frequency differenceresponsive means 39 closes its contacts 2I2 and completes an operatingcircuit for the rheostat motor I5I so as to decrease the secondaryresistance of the motor 20 and thereby effect an increase in the speedof the converter I4. This operating circuit for the motor I5I is fromthe positive terminal of the battery B to the conductor I41 in themanner just described, then through contacts 222 of frequency differenceresponsive means 39, conductor I48, limit switch I49 on rheostat 35,field winding I 50 and armature winding of motor IM to the negativeterminal of batterv B.

When the proper space relationship exists between the rotors of the twoconverters I4 and 22 so that the relay 83 is ener ized at the same timea predetermined phase and frequency difference relationship existsbetween the voltages of the s nchronous mac ine l? and the bus 3 so thatthe contacts I83 of the automatic synchronizer 4c are closed, anenergizing circuit is completed for the closing coil of the circuitbreaker I8 so that the synchronous machine I1 is connected to the bus 3.This energizing circuit for the closing coil of the circuit breaker i8is from the positive terminal of the battery B throu h contacts 5 ofrelay 5V, conductor lid. contacts I32 of relay ifii, conductor 1133, c.itacts ltd of relay as, con-- duct-or E35. contacts of automaticsynchronizer conductor i contacts is of relay con tacts 292% of reiayconductor E33, closing coil of circ it breaker to the negative terminalof ba cry 33%,

The opening of the auxiliary contacts 886 on the circuit breakerinterrupts the energizing circuit of the control relay wh ch in turn byo ening its contacts I53 and 868 renders the frenuencv differenceresponsive means 39 and the automatic synchronizei' till inoperative.The closing of the contacts I36 of the control relay 89 com le es anenergiz ng circuit for the control relav 88 from the positive terminalof the battery B throu h contacts II5 of relay 51, conductor H6.contacts l32 of'relay I21, conductor I33, auxiliary contacts I34 oncircuit breaker I6. conductor I35, winding of relay 88. contacts I36 ofrelay 89. conductor I31, auxiliary contacts 2I6 on circuit breaker I8 tothe negative terminalof batt'ery B.

The closing of the contacts I40 and HI of relay 88 renders the frequencydifference responsive means 36 and the automatic synchronizer 31operative by connecting them to the synchronous machine I5 and to thebus I. If the frequency of the synchronous machine I5 is higher than thefrequency of the bus I or is lower than this bus frequency, but thefrequency difference is less than a predetermined value, the frequencydifference responsive means 36 closes its contacts 2I1 and completes anenergizing circuit for the prime mover governing motor I1.I so that iteffects an increase in the frequency of the bus I. This energizingcircuit for the motor I1I is from the positive terminal of the battery Bthrough contacts II5 of relay 51, conductor II6, contacts I32 of relayI21, conductor I33, contacts 226 of relay 88, conductor 22I, auxiliarycontacts 222 on circuit breaker I8, conductor I15, contacts I16 of relay58, conductor I11, contacts 2I1 of frequency difference responsive means36, field winding I8I and armature winding of motor I1I to the ne ativeterminal of battery B.

If the frequency of the machine I5 is lower than the frequency of thebus I by more than a predetermined amount, the frequency differenceresponsive means 36 closes its contacts 2I8 and completes an operatingcircuit for the prime mover governing motor I1I so that it effects adecrease in the frequency of the bus I. This op erating circuit for themotor I1! is from the positive terminal of the battery B to conductorI11 in the manner just described, then through contacts 2 I 8 offrequency difference responsive means 38, field winding I18 and armaturewinding of motor IN to the negative terminal of battery B.

When the proper phase and frequency difference relations have beenestablished between the voltages of the synchronous machine I5 and thebus i in response to the operation of the frequency differenceresponsive means 36, the automatic synchronizer 31 closes its contactsI55 and completes an energizing circuit for the closing coil of circuitbreaker I6 so that the synchronous machine I5 is connected to the bus I.This energizing circuit for the closing coil of the circuit breaker I 6is from the positive terminal of the battery B through contacts II5 ofrelay 51., condoctor I I6, contacts I32 of relay I21, conductor 533,contacts I56 of relay 88, conductor I51, contacts of automaticsynchronizer 31, conductor i58, contacts I59 of rela 18, conductor I60,auxiliary contacts 223 on circuit breaker 58, conductor I62, closingcoil of circuit breaker to the ne ative terminal of the battery 33'.

The opening of the auxiliary contacts 534 on the circuit breaker iiiinterrupts the heretofore described circuit for the control relay 88,which in turn by open ng its contacts Mil and S45 renders the frequencydifference responsive means 36 and the automatic synchronizer 81inoperative to control the prime mover governing motor ii i.

Buses 1 and 2 energized and not tied tocether; and buses 3 and 4energized and not tied togather It will now be assumed that when theconverter I4 is being started not only are the switches 6 and 9 open sothat the buses I and 2 are not tied together, but also that the buses 3and 4 are separately energized and are neither t ed together nor insynchronism so that the contacts 43 of the synchronism check relay 42are open and therefore, the relay 46 is deenergized and its contacts 11are closed.

Whether or not the converter 22 is in service when the converter I4 isstarted under the abovementioned electric conditions of the buses, the

control apparatus operates in the same manner as heretofore described inconnection with the starting of the converter I4 when only the energizedbuses 3 and 4 are tied together, since under the assumed conditions theenergizing circuit for the control relay I3 remains completed throughcontacts 11 of relay 46 after the exciter voltage relay 85 opens itscontacts 15 in response to the exciter voltage building up to a,predetermined value. It will be noted that if the relay I3 is energizedafter the exciter relay 65 operates, the control relay 88 is energizedfirst to effect the synchronization' of the synchronous machine Iwhereas if the relay 13 is deenergized the control relay 89 is energizedfirst to effect the synchronization of the synchronous machine I1.

Buses 1 and 2 energized and not tied together; and bus 3 deenergizedUnder the above-mentioned electric conditions of the buses, thedeenergized bus 3 may be connected to the bus 4 while it is deenergizedor the bus 3 may be disconnected from the bus 4 while the latter isdeenergized or is energized either by the converter 22 or by some othersource. The operation of the control equipment for the converter I4,however, is the same under all of these difierent electric'conditions ofthe bus 4 because the sequence of operation of the control equipment isdetermined by the voltage relay 44 being in its deenergized position.

When the converter I4 is started under the above-mentioned electricconditions of the buses, it is accelerated to substantially synchronousspeed in the manner heretofore described, and then the control relay 88isenergized in response to the closing of the contacts I32 of the relayI21 in the same manner as heretofore described, except that theenergizing circuit of thecontrol relay 88 includes the contacts 225 ofthe deenergized voltage relay 44 which are connected in parallel withthe contacts I38 of the relay 13. The relay 88 then effects theoperation of the motor operated rheostat 35 and the-closing of thecircuit breaker I8 to connect the synchronous machine I5 to the bus I inthe same manner as when the converter I4 is started with the energizedbuses 3 and 4 connected together and the energized buses I and 2disconnected fromeach other, except that the heretofore describedenergizing circuit for the closing coil of the circuit breaker I6includes the contacts 228 of the deenergized voltage relay 44 which areconnected in parallel with the contacts IGI of the relay I3.

The opening of the auxiliary contacts I2I on the circuit breaker I6,when it connects the synchronous machine I5 to the bus I under theassumed electric conditions of the buses, interrupts the heretoforedescribed energizing circuit for the closing coil of the field switch34, since the parallel connected contacts I22 of the voltage relay 44are open. Therefore, the field switch 34 opens and disconnects the fieldwinding 32 of the synchronous machine I! from the exciter I9. Theclosing of the auxiliary contacts 221 on the field switch 34 completesan energizing circuit for the closing coil 0f the circuit breaker I8 sothat the unexcited synchronous machine I! is connected to the bus 3. Theenergizing circuit of the closing coil of the circuit breaker I8 is fromthe positive terminal of the battery B to conductor I33 in the mannerheretofore described, then through auxiliary contacts 228 on circuitbreaker I6, conductor 228, contacts 230 of voltage relay 44,

conductor 23I, contacts 221 of field switch 34, conductor I88, closingcoil of circuit breaker I8 to the negative terminal of battery B. Theclosing 01 the auxiliary contacts 232 on the circuit breaker I8completes an energizing circuit for the closing coil of the field switch34 so that the field winding 32 is again excited; This energizingcircuit is from the positive terminal of the battery B to conductor I28in the manner heretofore described, then through auxiliary contacts 232on circuit breaker I8, conductor I23, closing coil of field switch 34 tothe negative terminal of battery B.

Buses 1 and 2 energized and' tied together; bus 3 deenergized; and noother converter in operation of the converter I4 the voltage relay 44 isin its deenergized position.

Buses 1 and 2 energized and tied together; bu 3 deenergized; andconverter 22 in operation Under the above-mentioned electric conditionsof the buses, the bus 3 is disconnected from the bus 4. Therefore,during the starting operation of the converter I4, the voltage relay 44is in its deenergized position so that the converter is accelerated tosubstantiallysynchronous speed in the manner heretofore described, andthen the control relay 88 is energized in response to the closing of thecontacts I32 of the relay I21 in the same manneras when the bus 3 isdeenergized, the buses I and 2 are not tied together, and converter 22is not in operation.

Since however, both of the switches 6 and 8 are assumed to be closed,the relay 50 is deenergized during the starting operation of theconverter I4. Also, the energizing circuit of the relay I3 remainscompleted through the contacts 11 of relay 46 during the startingoperation of the converter I4 because both the contacts 43 of thesynchronism check relay 42 and the contacts 98 of the energized voltagerelay 45 are simultaneously open under the assumed conditions.Furthermore, as soon as the converter I4 has accelerated toapproximately synchronous speed so that the exciter relay 65 isoperated, the heretofore described circuit of the relay BI isinterrupted. .The relay 6| then closes its contacts 235 and completes anenergizing circuit for the control relay 10 through the contacts 236 ofthe deenergized relay 50. The opening of the contacts I59 of the relayI0 interrupts the heretofore described energizing circuit for theclosing coil of the circuit breaker I 6 through the contacts I55 of theautomatic synchronizer 31.

When th relay 88 becomes energized during the startingoperation of theconverter I 4, the closing of the contacts I40 and MI of the relay 88renders the frequency difference responsive means 36 operative in themanner heretofore described so that it controls the motor operatedrheostat 35 in the proper manner to bring the synchronou machine I intosynchronism with the bus I and so that th automatic synchronizer 31closes its contacts I55 when a predetermined phase and frequencyrelationship is established between the voltages of the synchronousmachine I5 and the bus I. Also, the closing of the contacts 239 of therelay 88 completes an energizing circuit for the control relay 80 fromthe positive terminal of the battery B at the substation B throughcontacts I99 of relay 9I, contacts 260 of relay 9!], contacts 248 ofrelay 1I, contacts 24I of relay 14, contact making device 83, pilot wire202, contact making device 82, conductor 243, contacts 238 of relay 13,contacts 231 of relay 10, conductor 205, contacts 239 of relay 88,winding of relay 80 and condenser 86 in parallel, pilot Wire 261,contacts 268 of relay 98, contacts 269 of relay 9I to the negativeterminal of battery B". The relay 80, therefore, can be energized onlywhen the positions of the rotors of the converters I4 and 22 are such asto effect the simultaneous closing of the contacts of the contact makingdevices 82 and 83.

When the proper space relationship exists between the rotors of the twoconverters I4 and 22 so that the relay 80 is energized at the same timthe contacts I55 of the automatic synchronizer 31 are closed, anenergizing circuit is completed for the closing coil of the circuitbreaker I6 so that the synchronous machine I5 is connected to the bus I.This energizing circuit for the closing 'coil of the circuit breaker i6is from the positive terminal of the battery B to conductor I33 in themanner heretofore described, then through contacts I56 of relay 88,conductor I51, contacts I55 of automatic synchronizer 31, conductor I58,contacts 244 of relay 10, contacts 245 of relay 13, contacts 246 ofrelay 80, conductor I62, closing coil of circuit breaker I6 to thenegative terminal of battery 13'.

The opening of the auxiliary contacts I2l of the circuit breaker I6effects the opening of the field switch 34, and then the circuit breakerI8 is closed to connect the unexcited synchronous machine i1 to the bus3, and the field switch 34 is subsequently reclosed to excite the fieldwinding 32 in the same manner as when the low frequency bus 3 isdeenergized and the buses I and 2 are not tied together.

Buses 1 and 2 energized and tied together; buses 3 and 4 energized andtied together; and converter 22 in operation During the startingoperation of the converter I4 under the above-mentioned conditions ofthe buses, the control relay 13 becomes deenergized as soon as theexciter voltage relay 65 open its contacts 15, and the relay 6I becomesdeenergized and effects the energization of the control relay 18 as soonas the exciter voltage relay 65 opens its contacts 63. Therefore, theconverter I4 is started, and the control relay 89 is energized to effectthe closing of the circuit breaker I8 and the connection of thesynchronous machine I1 to the bus 3 in the same manner as when theconverter is started with the buses I and 2 not tied together, the buses3 and 4 tied together, and the converter 22 is in operation.

The opening of the auxiliary contacts I66 of thecircuit breaker I8interrupts the energizing circuit of the control relay 8'9, and theclosing of the contacts I36 of the relay 89 completes the heretoforedescribed energizing circuit for the control relay 88 through theauxiliary contacts I34 on the open circuit breaker I6. Since the relay10 is energized when the relay 88 becomes energized under theabove-mentioned conditions, the closing of the contacts 220 of the relay88 renders the phase responsive arrangement 95 operative to control theframe shilting motor 2| so as to establish a predetermined phaserelation between the voltages of tne synchronous machine I5 and the busI.v If the voltage of the machine I5 leads the voltage of the bus I sotnat the contacts 96 of the phase responsive arrangement 95 are closed,an operating circuit is completed 101' the motor 2I to cause it torotate the frame of the machine I5 in tile proper direction to bring thevoltages of the machine I5 and the bus I into phase. This operatingcircuit is from the positive terminal of the battery B tothe conductorI33 in the manner heretofore described, tnen through contacts 220 ofrelay 88, conductor 22I, auxiliary contacts 248 on circuit breaker I8,contacts 249 of relay 13, conductor 250, contacts 25I of relay 10,conductor 252, auxiliary contacts 253 on circuit breaker I6, contacts 96of phase responsive arrangement 95, field winding254 and armaturewinding of motor 2I to the negative terminal of battery B. If thevoltage of the machine I5 lags the voltage of the bus I so that thecontacts 31 of the phase responsive arrangement are closed, an operatingcircuit is completed for the motor 2I to cause it to rotate the frame ofthe machine I5 in the opposite direction so as to bring the voltages ofthe machine I5 and the bus I into phase. This operating circuit is fromthe positive terminal of the battery B to the contacts 253 on thecircuit breaker I8 in the manner heretofore described, then throughcontacts 91 of the phase responsive arrangement 95, field winding 255and armature winding of motor 2I to the negative terminal of battery B.

When the voltages of the machine I5 and the bus I have been brought intosubstantially phase coincidence so that both of the contacts 98 and 99of the phase responsive arrangement 95 are simultaneously closed, anenergizing circuit is then completed for the closing coil of the circuitbreaker I6 so that the synchronous machine I5 is connected to the bus I.This energizing circuit is from the positive terminal of the battery Bto conductor I33 in the manner heretofore described, then throughcontacts I56 of relay 88, conductor I51, contacts 255 of relay .10,contacts 256 of relay 13, conductor 251, contacts 99 and 98 of phaseresponsive arrangement 95, conductor I62, closing coil of circuitbreaker I6 to the negative terminal of battery B.

The closing of the auxiliary contacts 228 on the circuit breaker I6completes an energizing circuit for the frame shifting motor 2I so thatit restores the frame of the machine I5 to its normal position andthereby causes the load to be equally divided between the two parallelconnected converters I4 and 22. This restoring circuit for the motor 2|is from the positive terminal of the battery B to conductor I33 in themanner heretofore described, then through auxiliary contacts 228 oncircuit breaker I6, conductor 229, auxiliary contacts 260 on circuitbreaker I8, conductor 26I, off-normal frame shifting contacts 262 andfield winding 255, or off-normal frame shifting contacts 263 and fieldwinding 254, depending upon the position of the frame shiftingmechanism, armature winding of motor 2I to the negative terminal ofbattery B. When the frame shifting mechanism is restored to its normalposition, this restoring circuit is interrupted at either the off-normalcontacts 262 or 263.

Buses 1 and 2 energized and tied together; buses 3 and 4 energized andtied together; and converter 22. not in operation ner as if theconverter were being started with the buses I and 2 disconnected.However, after the circuit breaker I6 is closed to connect thesynchronous machine I5 to the bus I and the control relay 89 isenergized, the frequency difference responsive means 39 cannot controlthe prime mover governing motor III to vary the frequency of the bus Ibecause the contacts I15 of the relay 50 are now open. Therefore, unlessthe synchronous machine I! happens to be in synchronism with the bus 3so that the contacts we of the automatic synchronizer 40 are closed, itis necessary for the operator at one of the substations to disconnectthe buses I and 2- from each other before the control equipment at thesubstation A can complete the starting operation of the converter It byautomatically closing the circuit breaker I8 and connecting thesynchronous machine If to the bus 3. The control apparatus for theconverter I4 is rendered inoperative to control the prime movergoverning motor I'II under the above-mentioned electric conditions ofthe buses because it might be objectionable to change the load divisionof the prime mover driven generators at the two substations under theseconditions.

Buses 1 and 2 energized and tied together; buses 3 and 4 energized andnot tied together; and converter 22 in operation Under theabove-mentioned electric conditions of the buses, the synchronousmachine I5 is synchronized during the starting operation of theconverter I4 in the same manner as when the buses I and 2 are tiedtogether, the converter 22 is in operation, and the bus 3 isdeenergized. After the circuit breaker I6 is closed, however, thefrequency difference responsive means 39 cannot control the prime movergoverning motor I'll to vary the frequency of the bus I because thecontacts I16 of the relay 50 ar open. Therefore, unless the synchronousmachine I? happens to be in synchronism with the bus I so that thecontacts I83 of the automatic synchronizer 40 are closed after thecircuit breaker I6 closes, it is necessary for the operator at one ofthe substations to disconnect the buses I and 2 from each other beforethe control apparatus for the converter II can automatically close thecircuit breaker I8 and thereby connect the synchronous machine H to thebus 3.

Disconnection of converter 14 The converter I4 can be taken out ofservice at any time by opening the switch I and effecting thedeenergization of the master relay 51. The closing of the contacts 266of relay completes an energizing circuit for the trip coil 261 of thecircuit breaker I6 through auxiliary contacts 268 on the circuit breakerI6 and conductor 269 and also an energizing circuit for the trip coil2'") of the circuit breaker I8 through the auxiliary contacts 2' on thecircuit breaker I8 and conductor 269. The closing of the contacts 212 ofthe relay 51 connects the conductor 28I to the positive terminal of thebattery B so that a circult is completed in the manner heretoforedescribed for the frame shifting motor 2i in case the frame of thesynchronous machine I5 is not in its normal position.

While I have, in accordance with the patent statutes, shown anddescribed my invention as applied to a particular system and asembodying various devices diagrammatically indicated, changes andmodifications will be obvious to those skilled in the art, and Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, two energized alternating current circuits ofdifferent frequencies, a synchronous frequency converter comprising twosynchronous machines, one of which is connected to one of said circuits,and means controlled by the difference between the frequencies of theother of said machines and the other of said circuits for varying thefrequency of one of said circuits to decrease said frequency difference.

2. In combination, two energized alternating current circuits ofdifierent frequencies,'a synchronous frequency converter comprisin twosynchronous machines, means for connecting one of said machines to oneof said circuits, and means responsive to the connection of said one ofsaid machines to said one of said circuits under predetermined electricconditions of said circuits for varying the frequency of one of saidcircuits in response to th difference between the frequencies of theother of said machines and the circuit to which said one of saidmachines is not connected.

3. In combination, two alternating current circuits of differentfrequencies, a prime mover driven generator connected to one of saidcircuits, means for energizing the other, circuit, a synchronousfrequency converter comprising two synchronous machines, means forsynchronizing one of said machines with one of said circuits, and meansresponsive to the completion of said synchronization for controlling thefrequency of said prime mover driven generator in response to thedifference between the frequencies of the other of said machines and thecircuit to which said one of said machines is not synchronized.

4. In combination, two alternating current circuits of differentfrequencies, a prime mover driven generator connected to one of saidcircuits, means for energizing the other circuit, a synchronousfrequency converter comprising two synchronous machines, means forsynchronizing one of said machines with one of said circuits, meansresponsive to the completion of said synchronization for controlling thefrequency of said prime mover driven generator in response to thedifference between the frequencies of the other of said machines and thecircuit to which said one of said machines is not synchronized, andautomatic synchronizing means for connecting said other of said machinesand said last mentioned dition of said circuits for sequentiallyconnecting said converter to said circuits in a different predeterminedsequence.

6. In combination, two alternating current circuits of differentfrequencies, a synchronous frequency converter, means responsive to bothof said circuits being energized while said converter is being startedfor effecting first the synchronization of said converter to apredetermined one of said circuits and then the synchronization of saidconverter with the other of said circuits, and means responsive toeither of said circuits being energized and the other of said circuitbeing deenergized while said converter is being started for effectingfirst the synchronization of said converter to the energizedcircuit andthen the connection of said converter to the deenergized circuit.

7. In combination, two alternating current circuits of differentfrequencies, a synchronous frequency converter comprising twosynchronous machines, means responsive to both of said circuits beingenergized while said converter is being started for effecting first thesynchronization of one of said machines to one of said circuits and thenthe variation in the frequency of one of said circuits in response tothe frequency difference between the other of said machines and thecircuit to which said one of said machines is not synchronized to effectthe synchronization of the said other machine to the last mentionedcircuit, and means responsive to said one of said circuits beingenergized and the other of said circuits being deenergized while saidconverter is being started for effecting first the synchronization ofsaid one of said machines to said one of said circuits and then theconnection of said other machine to the circuit to which said one ofsaid. machines is not connected while the field Winding of said othermachine is deenergized and then the energization of said field winding.

8. In combination, two alternatin current circuits of a predeterminedfrequency, means for interconnecting said circuits, two alternatingcurrent circuits of a different predetermined frequency, means forinterconnecting said last mentioned circuits, a synchronous converterinterconnecting a predetermined one of said circuits of a predeterminedfrequency and a predetermined one of said circuits of a differentpredetermined frequency, a second synchronous frequency converter, andmeans responsive to different electric conditions of said circuits forsequentially connecting said second converter to the other of saidcircuits in different orders.

9. In combination, two alternating current circuits of a predeterminedfrequency, means for interconnecting said circuits, two alternatingcurrent circuits of a different predetermined frequency, means forinterconnectin said last mentioned circuits, a synchronous converterinterconnecting a predetermined one of said circuits of a predeterminedfrequency and a predetermined 'one of said circuits of a differentpredetermined frequency, a second synchronous frequency convertercomprising a synchronous machine of said termined frequency, and meansresponsive to a different predetermined electric condition of saidcircuits for effecting the synchronization of said synchronous machinein the reverse order.

10. In combination, a synchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and an electriccircuit of a different predetermined frequency, a second electriccircuit of said predetermined frequency, a second electric circuit ofsaid different predetermined frequency, means for connecting saidcircuits of said predetermined frequency together, means for connectingsaid circuits of different predetermined frequency together, a secondsynchronous frequency converter, and means controlled by the electricconditions of said circuits for connecting said second converter betweensaid second electric circuit in different sequences depending upon theelectric conditions existing while said second converter is being placedin service.

11. In combination, a synchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and an electriccircuit of a different predetermined frequency, a second electriccircuit of said predetermined frequency, a second electric circuit ofsaid different predetermined frequency, means for connect said circuitsof said predetermined frequency together, means for connecting saidcircuits of different predetermined frequency together, a secondsynchronous frequency converter, and means controlled by the electricconditions of said circuits for connecting, said second converterfirstto said second electric circuit of said predetermined frequency andthen to said second electric circuit of said different predeterminedfrequency whenever said circuits of said predetermined frequency areenergized and connected together and for connecting said secondconverter first to said second electric circuit of said differentpredetermined frequency and then tos'aid second electric circuit of saidpredetermined frequency when said last mentioned circuit is notenergized while said second converter is being placed in service.

12. In combination, a synchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and an electriccircuit of a lower predetermined frequency, a second electric circuit ofsaid predetermined frequency, a second electric circuit of said lowerpredetermined frequency, means for interconnecting said circuits of saidpredetermined frequency, means for interconnecting said circuits of saidlower predetermined frequency, a second synchronous frequency converter,and means controlled by the electric conditions of said circuits forconnecting said second converter first to said second electric circuitof said lower predetermined frequency and then to said second electriccircuit of said predetermined frequency whenever both of said circuitsof said lower frequency are energized and connected together and forconnecting said second converter first to said second circuit of saidpredetermined frequency and then to said second circuit of said lowerpredetermined frequency when said last mentioned circuit is not en rized while said second converter is being placed in service.

13. In combination, a synchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and an electriccircuit of a lower predetermined frequency, a second electric circuit ofsaid predetermined frequency, a second electric circuit of said lowerprel determined frequency, means for interconnecting said circuits ofsaid predetermined frequency, m ans for interconnecting said circuits ofsaid lower predetermined frequency, a second syn= chronous frequencyconverter comprising a synchronous machine of said predeterminedfrequency and a synchronous machine of said lower predeterminedfrequency, and means controlled by the electric conditions of saidcircuits for first synchronizing said synchronous machine of said lowerpredetermined frequency to said second circuit of said lowerpredetermined frequency and aseqses tric circuit of a higherpredetermined frequency,

, asecond electric circuit of said predetermined then synchronizing saidsynchronous machine of 1 said predetermined frequency to said secondcircult of said predetermined frequency whenever both of said circuitsof said lower predetermined frequency are energized and connectedtogether and for first synchronizing said synchronous machine of saidpredetermined frequencyto said second circuit of said predeterminedfrequency and then connecting said synchronous machine of said lowerpredetermined frequency to said second circuit of said lowerpredetermined frequency when said last mentioned circuit is deenergizedwhile said second converter is being placed in service.

14. In combination, a synchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and an electriccircuit of a different predetermined frequency, a second-electriccircuit of said predetermined frequency, a second electric circuit ofsaid different predetermined frequency, a second synchronous frequencyconverter, means responsive to a predetermined space relationshipbetween the rotors of said converters for controlling the connection ofsaid second converter to said second electric circuit of saidpredetermined frequency, means responsive to a different spacerelationship between the rotors of said converter for controlling theconnection of said second converter to said second electric circuit ofsaid different predetermined frequency, an'd means controlled by theelectric conditions of said circuits for selectively controllingtheoperation of said connecting means. v

15. In combination, asynchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and an electriccircuit of a different predetermined frequency, a second electriccircuit of said predetermined frequency, a second electric circuit ofsaid different predetermined frequency, a second synchronous frequencyconverter, means responsive to a predetermined space relationshipbetween the rotors of said converters for controlling the connection ofsaid second converter to said second electric circuit of saidpredetermined frequency, means responsive to a different spacerelationship between the rotors of said converters for controlling theconnection of said second converter to said second electric circuit ofsaid different predetermined frequency, and means controlled by theelectric conditions of said circuits for effecting the operation of saidfirst mentioned space relationship responsive means whenever saidelectric circuits of said predetermined frequency are in synchronism andfor effecting the operation of said second mentioned space relationshipresponsive means when only said electric circuits of said differentpredetermined frequency are in synchronism.

16. In combination, a synchronous frequency converter interconnectedbetween an electric circuit of a predetermined frequency and anelecfrequency, a second electric circuit of said higher predeterminedfrequency, a second synchronous frequency converter, means responsive toa predetermined space relationship between the rotors of said convertersfor controlling the connection of said second converter to said secondelectric circuit of said predetermined frequency, means responsive to adifferent space relationship between the rotors of said converter forcontrolling the connection of said second converter to said secondelectric circuit of said higher predetermined frequency, and meanscontrolled by the electric conditions of said circuits for effecting theoperation of said first mentioned space relationship responsive meanswhenever said electric circuits of said predetermined frequency are insynchronism and for effecting the operation of said second mentionedspace relationship responsive means when only said electric circuits ofsaid higher predetermined frequency are in synchronism.

17. In combination, an alternating'current circuit of a predeterminedfrequency, a second alternating current circuit of a differentpredetermined frequency, a synchronous frequency converterinterconnected between said circuits and having a frame shiftingmechanism, means for maintaining said frame shift ng mechanism in apredetermined position while said converter is in operation, a secondfrequency converter having a frame shifting mechanism, means forinterconnecting said second frequency converter between said circuitsincluding means for varying said last mentioned frame shifting mechanismfrom a predetermined position corresponding to said predeterminedposition of said first mentioned frame shifting mechanism, and meansresponsive to the interconnection of said second converter between saidcircuits for restoring said second frame shifting mechanism to itspredetermined position.

18. In combination, an alternating current circuit of a predeterminedfrequency, a second alternating current circuit of a differentpredetermined frequency, a synchronous frequency converterinterconnected between said circuits, frame shifting mechanismassociated with said converter, means for maintaining said mechanfsm ina predetermined position while said converter is in operation, a secondfrequency converter having a frame shifting mechanism, means forsynchronizing said converter with one of said circuits, means forsynchronizing said converter with the other of said circuits includingmeans for varying the position of the frame shifting mechanism of saidsecond converter, and means responsive to the interconnection of saidsecond converter between said circuits for restoring the frame shiftingmechanism of said second converter to a predetermined positioncorresponding to said predetermined position of said first mentionedframe shifting mechanism.

\ and for connecting said other of said converters to said circuits inthe reverse sequence when said one of said converters is notinterconnected between said circuits.

20. In-combination, an electric circuit of predetermined frequency, asecond electric circuit 5 of a different predetermined frequency, twofrequency converters for interconnecting between said circuits,automatic starting and synchronizing means for said converters includingmeans responsive to a predetermined space relationship 10 electriccircuits.

HERMAN BANY.

